’ The Soft Foam Sword is useable on NPCs that are a trivial difficulty to your character. This means that it can only be used if the character is at least 20 levels higher than the NPC you’re targeting.
The sword has a couple of other limitations: it cannot be used in dungeon or raid instances and cannot be used on rare elite creatures.’
It could be that the level squish has made the 20 level higher thing more difficult
/edit I should’ve said that the 2 quoted paras are from the Support site.